In a thin-film transistor liquid crystal display (TFT-LCD), thin-film transistor (TFT), taken as a switching element of a digital circuit, plays a very important role.
Currently, in the manufacturing process of a TFT-LCD array substrate, single-slit mask, gray-tone mask or half-tone mask are generally adopted for implementing the source/drain metal mask (SD mask) process. When a single-slit mask is adopted for SD mask process, photoresist on channel areas between source electrodes and drain electrodes is exposed by slit diffraction. But as channels between the source electrodes and the drain electrodes are relatively narrow, if exposed light has too low light intensity after slit diffraction and is underexposed, the channels between the source electrodes and the drain electrodes of the TFT-LCD array substrate tend to have metal bridging phenomenon after subsequent development and etching; and if the exposed light has too high light intensity after slit diffraction and is overexposed, the channels between the source electrodes and the drain electrodes may also have semiconductor missing phenomenon after subsequent development and etching. No matter whether there is metal bridging phenomenon or semiconductor missing phenomenon on the channels between the source electrodes and the drain electrodes, the TFTs could not operate normally and even could not operate. Therefore, in the SD mask process by adoption of the single-slit mask, the light intensity of the exposed light which is diffracted when running through slits corresponding to the channel areas between the source electrodes and the drain electrodes must be properly controlled.
More specifically, as illustrated in FIG. 1, in the TFT-LCD array substrate, it is well-known that the distribution density of the TFTs in a non-display area 5 (e.g., a peripheral wiring area) is much higher than the distribution density of the TFTs in a display area 6 (namely a pixel area). Therefore, as for photoresist on a source/drain metal layer, taking positive photoresist as an example, in the development process after exposure, the consumption of a developer in the non-display area 5 in unit time and unit area is much lower than the consumption of the developer in the display area 6, so that the concentration of the developer in the non-display area 5 is higher than the concentration of the developer in the display area 6. Thus, the photoresist on the channel areas between the source electrodes and the drain electrodes of the TFTs in the non-display area 5 tends to be thin after development, and semiconductors on the channels between the source electrodes and the drain electrodes tend to miss after etching, so that the source electrodes and the drain electrodes cannot be communicated, and hence the TFTs in the non-display area 5 of the TFT-LCD cannot operate, and finally the display area 6 cannot display normally.